Zoom lens system, imaging device and camera

ABSTRACT

A high-performance zoom lens system which is compact and has a wide view angle at a wide-angle limit and a high zooming ratio in a balanced manner, in order from an object side to an image side, comprising a first lens unit having positive optical power, a second lens unit having negative optical power, a third lens unit having positive optical power, and a fourth lens unit having positive optical power, wherein the first lens unit is composed of at most two lens elements, the second lens unit is composed of two lens elements, the third lens unit is composed of three lens elements, in order from the object side to the image side, including an object side lens element having positive optical power, a lens element having negative optical power, and an image side lens element having positive optical power, and the conditions: f T /f W &gt;6.0 and ω W ≧30 (f T : a focal length of the entire system at a telephoto limit, f W : a focal length of the entire system at a wide-angle limit, ω W : a half view angle at a wide-angle limit) are satisfied; an imaging device; and a camera are provided.

TECHNICAL FIELD

The present invention relates to a zoom lens system, an imaging deviceand a camera. In particular, the present invention relates to: ahigh-performance zoom lens system which is compact and has a wide viewangle at a wide-angle limit and a high zooming ratio in a balancedmanner; an imaging device employing the zoom lens system; and a thin andcompact camera employing the imaging device.

BACKGROUND ART

There are extremely strong demands for size reduction and performanceimprovement in digital still cameras and digital video cameras (simplyreferred to as digital cameras, hereinafter) having an image sensor forperforming photoelectric conversion. In particular, from a conveniencepoint of view, digital cameras are strongly requested that employ a zoomlens system having a high zooming ratio and still covering a widefocal-length range from a wide angle condition to a highly telephotocondition. On the other hand, in recent years, zoom lens systems arealso desired that have a wide angle range where the photographing fieldis large.

As zoom lens systems having a high zooming ratio and zoom lens systemshaving a wide angle range as described above, various kinds of zoomlenses having a four-unit construction of positive, negative, positiveand positive have conventionally been proposed, which each comprises, inorder from the object side to the image side, a first lens unit havingpositive optical power, a second lens unit having negative opticalpower, a third lens unit having positive optical power, and a fourthlens unit having positive optical power.

Japanese Laid-Open Patent Publication No. 2008-146016 discloses a zoomlens having the above-mentioned four-unit construction of positive,negative, positive and positive, in which at the time of magnificationchange from a wide-angle limit to a telephoto limit, at least a firstlens unit, a second lens unit, and a third lens unit are moved andthereby the intervals between the respective lens units are changed, thesecond lens unit is composed of at most three lenses, and the relationbetween the ratio of the values of lateral magnification of the secondlens unit at a telephoto limit and a wide-angle limit and the ratio ofthe values of lateral magnification of the third lens unit at atelephoto limit and a wide-angle limit is set forth.

Japanese Laid-Open Patent Publication No. 2008-122880 discloses a zoomlens having the above-mentioned four-unit construction of positive,negative, positive and positive, and having a zooming ratio of 3 to 12,in which a second lens unit is composed of at most three lenses, abi-concave negative lens is arranged on the most object side in thesecond lens unit, and the shape factor of the bi-concave negative lensis set forth.

Japanese Laid-Open Patent Publication No. 2008-122879 discloses a zoomlens having the above-mentioned four-unit construction of positive,negative, positive and positive, in which a first lens unit is composedof a negative lens and a positive lens, and the shape factor of thepositive lens is set forth.

Japanese Laid-Open Patent Publication No. 2008-052116 discloses a zoomlens having the above-mentioned four-unit construction of positive,negative, positive and positive, in which a first lens unit is composedof a positive lens and a negative lens, a second lens unit is composedof, in order from the object side, a negative lens and a positive lens,and a refractive index and an Abbe number of the negative lens in thesecond lens unit are set forth.

Japanese Laid-Open Patent Publication No. 2008-052113 discloses a zoomlens having the above-mentioned four-unit construction of positive,negative, positive and positive, and having a zooming ratio of 3.8 to10, in which a second lens unit includes a bi-concave negative lens onthe most object side, the entire second lens unit is composed of at mosttwo negative lenses and a positive lens, and the shape factor of thebi-concave negative lens is set forth.

Japanese Laid-Open Patent Publication No. 2008-052110 discloses a zoomlens having the above-mentioned four-unit construction of positive,negative, positive and positive, in which a second lens unit is composedof, in order from the object side, a negative lens and a positive lens,and a refractive index and an Abbe number of the positive lens are setforth.

Japanese Laid-Open Patent Publication No. 2007-328178 discloses a zoomlens having the above-mentioned four-unit construction of positive,negative, positive and positive, in which a first lens unit is composedof, in order from the object side, a negative lens and a positive lens,a second lens unit is composed of, in order from the object side, anegative lens and a positive lens, a third lens unit is composed of atmost three lenses including a positive lens and a negative lens, and afourth lens unit is composed of a positive lens.

Japanese Laid-Open Patent Publication No. 2007-256452 discloses a zoomlens having the above-mentioned four-unit construction of positive,negative, positive and positive, in which a third lens unit is composedof, in order from the object side, a first positive lens, a secondbi-concave negative lens, and a third negative lens, and at the time ofmagnification change, the interval between a first lens unit and asecond lens unit is greater and the interval between the second lensunit and the third lens unit is smaller at a telephoto limit than at awide-angle limit.

Japanese Laid-Open Patent Publication No. 2007-240747 discloses a zoomlens having the above-mentioned four-unit construction of positive,negative, positive and positive, in which a first lens unit is composedof, in order from the object side, two lenses, i.e., a negative lens anda positive lens; a second lens unit is composed of, in order from theobject side, two lenses, i.e., a negative lens and a positive lens; athird lens unit is composed of, in order from the object side, threelenses, i.e., a positive lens, a positive lens, and a negative lens; afourth lens unit is composed of a positive lens; at the time ofmagnification change, the interval between the first lens unit and thesecond lens unit is greater at a telephoto limit than at a wide-anglelimit, and the third lens unit is located closer to the object side sothat the interval between the third lens unit and the second lens unitdecreases; a brightness diaphragm, which moves in the direction alongthe optical axis at the time of magnification change, is arrangedbetween the second lens unit and the third lens unit; and the brightnessdiaphragm is located closer to the object side at a telephoto limit thanat a wide-angle limit.

Japanese Laid-Open Patent Publication No. 2007-171371 discloses a zoomlens having the above-mentioned four-unit construction of positive,negative, positive and positive, in which a first lens unit is locatedcloser to the object side at a telephoto limit than at a wide-anglelimit; the interval between the first lens unit and a second lens unitis greater, the interval between the second lens unit and a third lensunit is smaller, and the interval between the third lens unit and afourth lens unit is greater at a telephoto limit than at a wide-anglelimit; the first lens unit is composed of a negative lens and a positivelens; the second lens unit is composed of, in order from the object sideto the image side, a negative lens and a positive lens; and the ratiobetween the focal length of the negative lens in the second lens unit orthe focal length of the second lens unit, and the focal length of theentire lens system at a wide-angle limit is set forth.

Japanese Laid-Open Patent Publication No. 2008-172321 discloses animaging device comprising: a zoom lens which includes theabove-mentioned four-unit construction of positive, negative, positiveand positive, and performs zooming from a wide-angle limit to atelephoto limit with the intervals between a plurality of lens unitsbeing varied; an image sensor; and an image recovery unit, in which therelations among the maximum length of the zoom lens along the opticalaxis from its most-object-side refractive surface to its imagingsurface, the focal lengths of the entire system at a wide-angle limitand a telephoto limit, the minimum F-number at a telephoto limit, andthe half of the diagonal length of an effective imaging range on theimaging surface, are set forth.

CITATION LIST Patent Literature

-   [PTL 1] Japanese Laid-Open Patent Publication No. 2008-146016-   [PTL 2] Japanese Laid-Open Patent Publication No. 2008-122880-   [PTL 3] Japanese Laid-Open Patent Publication No. 2008-122879-   [PTL 4] Japanese Laid-Open Patent Publication No. 2008-052116-   [PTL 5] Japanese Laid-Open Patent Publication No. 2008-052113-   [PTL 6] Japanese Laid-Open Patent Publication No. 2008-052110-   [PTL 7] Japanese Laid-Open Patent Publication No. 2007-328178-   [PTL 8] Japanese Laid-Open Patent Publication No. 2007-256452-   [PTL 9] Japanese Laid-Open Patent Publication No. 2007-240747-   [PTL 10] Japanese Laid-Open Patent Publication No. 2007-171371-   [PTL 11] Japanese Laid-Open Patent Publication No. 2008-172321

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Each of the zoom lenses disclosed in the respective patent literaturesis miniaturized to such an extent that it can be applied to a thin andcompact digital camera, but cannot meet the recent demands in terms ofachieving a good balance between the view angle at a wide-angle limitand the zooming ratio.

The object of the present invention is to provide: a high-performancezoom lens system which is compact and has a wide view angle at awide-angle limit and a high zooming ratio in a balanced manner; animaging device employing the zoom lens system; and a thin and compactcamera employing the imaging device.

Solution to the Problem

One of the above-described objects is achieved by the following zoomlens system. That is, the present invention relates to:

a zoom lens system, in order from an object side to an image side,comprising a first lens unit having positive optical power, a secondlens unit having negative optical power, a third lens unit havingpositive optical power, and a fourth lens unit having positive opticalpower, wherein

the first lens unit is composed of at most two lens elements,

the second lens unit is composed of two lens elements,

the third lens unit is composed of three lens elements, in order fromthe object side to the image side, including an object side lens elementhaving positive optical power, a lens element having negative opticalpower, and an image side lens element having positive optical power, and

the following conditions (b-1) and (a-2) are satisfied:f _(T) /f _(W)>6.0  (b-1)ω_(W)≧30  (a-2)

where,

f_(T) is a focal length of the entire system at a telephoto limit,

f_(W) is a focal length of the entire system at a wide-angle limit, and

ω_(W) is a half view angle (°) at a wide-angle limit.

One of the above-described objects is achieved by the following imagingdevice. That is, the present invention relates to:

an imaging device capable of outputting an optical image of an object asan electric image signal, comprising:

a zoom lens system that forms an optical image of the object; and

an image sensor that converts the optical image formed by the zoom lenssystem into the electric image signal, wherein

the zoom lens system, in order from an object side to an image side,comprises a first lens unit having positive optical power, a second lensunit having negative optical power, a third lens unit having positiveoptical power, and a fourth lens unit having positive optical power,wherein

the first lens unit is composed of at most two lens elements,

the second lens unit is composed of two lens elements,

the third lens unit is composed of three lens elements, in order fromthe object side to the image side, including an object side lens elementhaving positive optical power, a lens element having negative opticalpower, and an image side lens element having positive optical power, and

the following conditions (b-1) and (a-2) are satisfied:f _(T) /f _(W)>6.0  (b-1)ω_(W)≧30  (a-2)

where,

f_(T) is a focal length of the entire system at a telephoto limit,

f_(W) is a focal length of the entire system at a wide-angle limit, and

ω_(W) is a half view angle (°) at a wide-angle limit.

One of the above-described objects is achieved by the following camera.That is, the present invention relates to:

a camera for converting an optical image of an object into an electricimage signal and then performing at least one of displaying and storingof the converted image signal, comprising:

an imaging device including a zoom lens system that forms the opticalimage of the object and an image sensor that converts the optical imageformed by the zoom lens system into the electric image signal, wherein

the zoom lens system, in order from an object side to an image side,comprises a first lens unit having positive optical power, a second lensunit having negative optical power, a third lens unit having positiveoptical power, and a fourth lens unit having positive optical power,wherein

the first lens unit is composed of at most two lens elements,

the second lens unit is composed of two lens elements,

the third lens unit is composed of three lens elements, in order fromthe object side to the image side, including an object side lens elementhaving positive optical power, a lens element having negative opticalpower, and an image side lens element having positive optical power, and

the following conditions (b-1) and (a-2) are satisfied:f _(T) /f _(W)>6.0  (b-1)ω_(W)≧30  (a-2)

where,

f_(T) is a focal length of the entire system at a telephoto limit,

f_(W) is a focal length of the entire system at a wide-angle limit, and

ω_(W) is a half view angle (°) at a wide-angle limit.

Effects of the Invention

According to the present invention, it is possible to provide: ahigh-performance zoom lens system which is compact and has a wide viewangle at a wide-angle limit and a high zooming ratio in a balancedmanner; an imaging device employing the zoom lens system; and a thin andcompact camera employing the imaging device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 1 (Example 1).

FIG. 2 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Example 1.

FIG. 3 is a lateral aberration diagram of a zoom lens system accordingto Example 1 at a telephoto limit in a basic state where image blurcompensation is not performed and in a blur compensation state.

FIG. 4 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 2 (Example 2).

FIG. 5 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Example 2.

FIG. 6 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 3 (Example 3).

FIG. 7 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Example 3.

FIG. 8 is a lateral aberration diagram of a zoom lens system accordingto Example 3 at a telephoto limit in a basic state where image blurcompensation is not performed and in a blur compensation state.

FIG. 9 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 4 (Example 4).

FIG. 10 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Example 4.

FIG. 11 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 5 (Example 5).

FIG. 12 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Example 5.

FIG. 13 is a lateral aberration diagram of a zoom lens system accordingto Example 5 at a telephoto limit in a basic state where image blurcompensation is not performed and in a blur compensation state.

FIG. 14 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 6 (Example 6).

FIG. 15 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Example 6.

FIG. 16 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 7 (Example 7).

FIG. 17 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Example 7.

FIG. 18 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 8 (Example 8).

FIG. 19 is a longitudinal aberration diagram of an infinity in-focuscondition of a zoom lens system according to Example 8.

FIG. 20 is a schematic construction diagram of a digital still cameraaccording to Embodiment 9.

EMBODIMENTS OF THE INVENTION Embodiments 1 to 8

FIGS. 1, 4, 6, 9, 11, 14, 16 and 18 are lens arrangement diagrams ofzoom lens systems according to Embodiments 1 to 8, respectively.

Each of FIGS. 1, 4, 6, 9, 11, 14, 16 and 18 shows a zoom lens system inan infinity in-focus condition. In each Fig., part (a) shows a lensconfiguration at a wide-angle limit (in the minimum focal lengthcondition: focal length f_(W)), part (b) shows a lens configuration at amiddle position (in an intermediate focal length condition: focal lengthf_(M)=√(f_(W)*f_(T))), and part (c) shows a lens configuration at atelephoto limit (in the maximum focal length condition: focal lengthf_(T)). Further, in each Fig., an arrow of straight or curved lineprovided between part (a) and part (b) indicates the movement of eachlens unit from a wide-angle limit through a middle position to atelephoto limit. Moreover, in each Fig., an arrow imparted to a lensunit indicates focusing from an infinity in-focus condition to aclose-object in-focus condition. That is, the arrow indicates the movingdirection at the time of focusing from an infinity in-focus condition toa close-object in-focus condition.

The zoom lens system according to each embodiment, in order from theobject side to the image side, comprises a first lens unit G1 havingpositive optical power, a second lens unit G2 having negative opticalpower, a third lens unit G3 having positive optical power, and a fourthlens unit having positive optical power. Then, in zooming, theindividual lens units move in a direction along the optical axis suchthat intervals between the lens units, that is, the interval between thefirst lens unit and the second lens unit, the interval between thesecond lens unit and the third lens unit, and the interval between thethird lens unit and the fourth lens unit should all vary. In the zoomlens system according to each embodiment, since these lens units arearranged in the desired optical power configuration, high opticalperformance is maintained and still size reduction is achieved in theentire lens system.

Further, in FIGS. 1, 4, 6, 9, 11, 14, 16 and 18, an asterisk “*”imparted to a particular surface indicates that the surface is aspheric.In each Fig., symbol (+) or (−) imparted to the symbol of each lens unitcorresponds to the sign of the optical power of the lens unit. In eachFig., the straight line located on the most right-hand side indicatesthe position of the image surface S. On the object side relative to theimage surface S (that is, between the image surface S and the most imageside lens surface of the fourth lens unit G4), a plane parallel plate Pequivalent to an optical low-pass filter or a face plate of an imagesensor is provided.

Further, in FIGS. 1, 4, 6, 9, 11, 14, 16 and 18, an aperture diaphragm Ais provided on the most object side in the third lens unit G3. Inzooming from a wide-angle limit to a telephoto limit at the time ofimage taking, the aperture diaphragm A moves along the optical axisintegrally with the third lens unit G3.

As shown in FIG. 1, in the zoom lens system according to Embodiment 1,the first lens unit G1, in order from the object side to the image side,comprises a negative meniscus first lens element L1 with the convexsurface facing the object side; and a positive meniscus second lenselement L2 with the convex surface facing the object side. The firstlens element L1 and the second lens element L2 are cemented with eachother.

In the zoom lens system according to Embodiment 1, the second lens unitG2, in order from the object side to the image side, comprises abi-concave third lens element L3; and a positive meniscus fourth lenselement L4 with the convex surface facing the object side. The thirdlens element L3 has two aspheric surfaces.

In the zoom lens system according to Embodiment 1, the third lens unitG3, in order from the object side to the image side, comprises apositive meniscus fifth lens element L5 with the convex surface facingthe object side; a negative meniscus sixth lens element L6 with theconvex surface facing the object side; and a bi-convex seventh lenselement L7. Among these, the fifth lens element L5 and the sixth lenselement L6 are cemented with each other. Further, the fifth lens elementL5 has an aspheric object side surface.

In the zoom lens system according to Embodiment 1, the fourth lens unitG4 comprises solely a bi-convex eighth lens element L8. The eighth lenselement L8 has an aspheric object side surface.

In the zoom lens system according to Embodiment 1, a plane parallelplate P is provided on the object side relative to the image surface S(between the image surface S and the eighth lens element L8).

In the zoom lens system according to Embodiment 1, in zooming from awide-angle limit to a telephoto limit at the time of image taking, thefirst lens unit G1 and the third lens unit G3 move to the object side,the second lens unit G2 moves to the image side with locus of a convexto the image side, and the fourth lens unit G4 moves to the image sidewith locus of a convex to the object side. That is, in zooming, theindividual lens units move along the optical axis such that the intervalbetween the second lens unit G2 and the third lens unit G3 shoulddecrease.

As shown in FIG. 4, in the zoom lens system according to Embodiment 2,the first lens unit G1, in order from the object side to the image side,comprises a negative meniscus first lens element L1 with the convexsurface facing the object side; and a positive meniscus second lenselement L2 with the convex surface facing the object side. The firstlens element L1 and the second lens element L2 are cemented with eachother.

In the zoom lens system according to Embodiment 2, the second lens unitG2, in order from the object side to the image side, comprises abi-concave third lens element L3; and a positive meniscus fourth lenselement L4 with the convex surface facing the object side. The thirdlens element L3 has two aspheric surfaces.

In the zoom lens system according to Embodiment 2, the third lens unitG3, in order from the object side to the image side, comprises apositive meniscus fifth lens element L5 with the convex surface facingthe object side; a negative meniscus sixth lens element L6 with theconvex surface facing the object side; and a positive meniscus seventhlens element L7 with the convex surface facing the object side. Amongthese, the fifth lens element L5 and the sixth lens element L6 arecemented with each other. Further, the fifth lens element L5 has anaspheric object side surface.

In the zoom lens system according to Embodiment 2, the fourth lens unitG4 comprises solely a bi-convex eighth lens element L8. The eighth lenselement L8 has an aspheric object side surface.

In the zoom lens system according to Embodiment 2, a plane parallelplate P is provided on the object side relative to the image surface S(between the image surface S and the eighth lens element L8).

In the zoom lens system according to Embodiment 2, in zooming from awide-angle limit to a telephoto limit at the time of image taking, thefirst lens unit G1 and the third lens unit G3 move to the object side,the second lens unit G2 moves to the image side with locus of a convexto the image side, and the fourth lens unit G4 moves to the image sidewith locus of a convex to the object side. That is, in zooming, theindividual lens units move along the optical axis such that the intervalbetween the second lens unit G2 and the third lens unit G3 shoulddecrease.

As shown in FIG. 6, in the zoom lens system according to Embodiment 3,the first lens unit G1, in order from the object side to the image side,comprises a negative meniscus first lens element L1 with the convexsurface facing the object side; and a positive meniscus second lenselement L2 with the convex surface facing the object side. The firstlens element L1 and the second lens element L2 are cemented with eachother.

In the zoom lens system according to Embodiment 3, the second lens unitG2, in order from the object side to the image side, comprises abi-concave third lens element L3; and a positive meniscus fourth lenselement L4 with the convex surface facing the object side. The thirdlens element L3 has two aspheric surfaces.

In the zoom lens system according to Embodiment 3, the third lens unitG3, in order from the object side to the image side, comprises apositive meniscus fifth lens element L5 with the convex surface facingthe object side; a negative meniscus sixth lens element L6 with theconvex surface facing the object side; and a bi-convex seventh lenselement L7. Among these, the fifth lens element L5 and the sixth lenselement L6 are cemented with each other. Further, the fifth lens elementL5 has an aspheric object side surface.

In the zoom lens system according to Embodiment 3, the fourth lens unitG4 comprises solely a bi-convex eighth lens element L8. The eighth lenselement L8 has an aspheric object side surface.

In the zoom lens system according to Embodiment 3, a plane parallelplate P is provided on the object side relative to the image surface S(between the image surface S and the eighth lens element L8).

In the zoom lens system according to Embodiment 3, in zooming from awide-angle limit to a telephoto limit at the time of image taking, thefirst lens unit G1 and the third lens unit G3 move to the object side,the second lens unit G2 moves to the image side with locus of a convexto the image side, and the fourth lens unit G4 moves to the image sidewith locus of a convex to the object side. That is, in zooming, theindividual lens units move along the optical axis such that the intervalbetween the second lens unit G2 and the third lens unit G3 shoulddecrease.

As shown in FIG. 9, in the zoom lens system according to Embodiment 4,the first lens unit G1, in order from the object side to the image side,comprises a negative meniscus first lens element L1 with the convexsurface facing the object side; and a positive meniscus second lenselement L2 with the convex surface facing the object side. The firstlens element L1 and the second lens element L2 are cemented with eachother.

In the zoom lens system according to Embodiment 4, the second lens unitG2, in order from the object side to the image side, comprises abi-concave third lens element L3; and a positive meniscus fourth lenselement L4 with the convex surface facing the object side. The thirdlens element L3 has two aspheric surfaces.

In the zoom lens system according to Embodiment 4, the third lens unitG3, in order from the object side to the image side, comprises apositive meniscus fifth lens element L5 with the convex surface facingthe object side; a negative meniscus sixth lens element L6 with theconvex surface facing the object side; and a bi-convex seventh lenselement L7. Among these, the fifth lens element L5 and the sixth lenselement L6 are cemented with each other. The fifth lens element L5 hasan aspheric object side surface.

In the zoom lens system according to Embodiment 4, the fourth lens unitG4 comprises solely a positive meniscus eighth lens element L8 with theconvex surface facing the object side. The eighth lens element L8 has anaspheric object side surface.

In the zoom lens system according to Embodiment 4, a plane parallelplate P is provided on the object side relative to the image surface S(between the image surface S and the eighth lens element L8).

In the zoom lens system according to Embodiment 4, in zooming from awide-angle limit to a telephoto limit at the time of image taking, thefirst lens unit G1 and the third lens unit G3 move to the object side,the second lens unit G2 moves to the image side with locus of a convexto the image side, and the fourth lens unit G4 moves to the image sidewith locus of a convex to the object side. That is, in zooming, theindividual lens units move along the optical axis such that the intervalbetween the second lens unit G2 and the third lens unit G3 shoulddecrease.

As shown in FIG. 11, in the zoom lens system according to Embodiment 5,the first lens unit G1, in order from the object side to the image side,comprises a negative meniscus first lens element L1 with the convexsurface facing the object side; and a positive meniscus second lenselement L2 with the convex surface facing the object side. The firstlens element L1 and the second lens element L2 are cemented with eachother. Further, the second lens element L2 has an aspheric image sidesurface.

In the zoom lens system according to Embodiment 5, the second lens unitG2, in order from the object side to the image side, comprises abi-concave third lens element L3; and a positive meniscus fourth lenselement L4 with the convex surface facing the object side. The thirdlens element L3 has two aspheric surfaces.

In the zoom lens system according to Embodiment 5, the third lens unitG3, in order from the object side to the image side, comprises apositive meniscus fifth lens element L5 with the convex surface facingthe object side; a negative meniscus sixth lens element L6 with theconvex surface facing the object side; and a bi-convex seventh lenselement L7. Among these, the fifth lens element L5 and the sixth lenselement L6 are cemented with each other. The fifth lens element L5 hasan aspheric object side surface.

In the zoom lens system according to Embodiment 5, the fourth lens unitG4 comprises solely a positive meniscus eighth lens element L8 with theconvex surface facing the object side. The eighth lens element L8 has anaspheric object side surface.

In the zoom lens system according to Embodiment 5, a plane parallelplate P is provided on the object side relative to the image surface S(between the image surface S and the eighth lens element L8).

In the zoom lens system according to Embodiment 5, in zooming from awide-angle limit to a telephoto limit at the time of image taking, thefirst lens unit G1 and the third lens unit G3 move to the object side,the second lens unit G2 moves to the image side, and the fourth lensunit G4 moves to the image side with locus of a convex to the objectside. That is, in zooming, the individual lens units move along theoptical axis such that the interval between the second lens unit G2 andthe third lens unit G3 should decrease.

As shown in FIG. 14, in the zoom lens system according to Embodiment 6,the first lens unit G1, in order from the object side to the image side,comprises a negative meniscus first lens element L1 with the convexsurface facing the object side; and a positive meniscus second lenselement L2 with the convex surface facing the object side. The firstlens element L1 and the second lens element L2 are cemented with eachother. Further, the second lens element L2 has an aspheric image sidesurface.

In the zoom lens system according to Embodiment 6, the second lens unitG2, in order from the object side to the image side, comprises abi-concave third lens element L3; and a positive meniscus fourth lenselement L4 with the convex surface facing the object side. The thirdlens element L3 has two aspheric surfaces.

In the zoom lens system according to Embodiment 6, the third lens unitG3, in order from the object side to the image side, comprises apositive meniscus fifth lens element L5 with the convex surface facingthe object side; a negative meniscus sixth lens element L6 with theconvex surface facing the object side; and a bi-convex seventh lenselement L7. Among these, the fifth lens element L5 and the sixth lenselement L6 are cemented with each other. Further, the fifth lens elementL5 has an aspheric object side surface.

In the zoom lens system according to Embodiment 6, the fourth lens unitG4 comprises solely a bi-convex eighth lens element L8. The eighth lenselement L8 has an aspheric object side surface.

In the zoom lens system according to Embodiment 6, a plane parallelplate P is provided on the object side relative to the image surface S(between the image surface S and the eighth lens element L8).

In the zoom lens system according to Embodiment 6, in zooming from awide-angle limit to a telephoto limit at the time of image taking, thefirst lens unit G1 and the third lens unit G3 move to the object side,the second lens unit G2 moves to the image side, and the fourth lensunit G4 moves to the image side with locus of a convex to the objectside. That is, in zooming, the individual lens units move along theoptical axis such that the interval between the second lens unit G2 andthe third lens unit G3 should decrease.

As shown in FIG. 16, in the zoom lens system according to Embodiment 7,the first lens unit G1, in order from the object side to the image side,comprises a negative meniscus first lens element L1 with the convexsurface facing the object side; and a positive meniscus second lenselement L2 with the convex surface facing the object side. The firstlens element L1 and the second lens element L2 are cemented with eachother.

In the zoom lens system according to Embodiment 7, the second lens unitG2, in order from the object side to the image side, comprises abi-concave third lens element L3; and a positive meniscus fourth lenselement L4 with the convex surface facing the object side. The thirdlens element L3 has two aspheric surfaces.

In the zoom lens system according to Embodiment 7, the third lens unitG3, in order from the object side to the image side, comprises apositive meniscus fifth lens element L5 with the convex surface facingthe object side; a negative meniscus sixth lens element L6 with theconvex surface facing the object side; and a bi-convex seventh lenselement L7. Among these, the fifth lens element L5 and the sixth lenselement L6 are cemented with each other. Further, the fifth lens elementL5 has an aspheric object side surface.

In the zoom lens system according to Embodiment 7, the fourth lens unitG4 comprises solely a bi-convex eighth lens element L8. The eighth lenselement L8 has an aspheric object side surface.

In the zoom lens system according to Embodiment 7, a plane parallelplate P is provided on the object side relative to the image surface S(between the image surface S and the eighth lens element L8).

In the zoom lens system according to Embodiment 7, in zooming from awide-angle limit to a telephoto limit at the time of image taking, thefirst lens unit G1 and the third lens unit G3 move to the object side,the second lens unit G2 moves to the image side with locus of a convexto the image side, and the fourth lens unit G4 moves to the image sidewith locus of a convex to the object side. That is, in zooming, theindividual lens units move along the optical axis such that the intervalbetween the second lens unit G2 and the third lens unit G3 shoulddecrease.

As shown in FIG. 18, in the zoom lens system according to Embodiment 8,the first lens unit G1, in order from the object side to the image side,comprises a negative meniscus first lens element L1 with the convexsurface facing the object side; and a positive meniscus second lenselement L2 with the convex surface facing the object side. The firstlens element L1 and the second lens element L2 are cemented with eachother.

In the zoom lens system according to Embodiment 8, the second lens unitG2, in order from the object side to the image side, comprises abi-concave third lens element L3; and a positive meniscus fourth lenselement L4 with the convex surface facing the object side. The thirdlens element L3 has two aspheric surfaces.

In the zoom lens system according to Embodiment 8, the third lens unitG3, in order from the object side to the image side, comprises apositive meniscus fifth lens element L5 with the convex surface facingthe object side; a negative meniscus sixth lens element L6 with theconvex surface facing the object side; and a bi-convex seventh lenselement L7. Among these, the fifth lens element L5 and the sixth lenselement L6 are cemented with each other. Further, the fifth lens elementL5 has an aspheric object side surface.

In the zoom lens system according to Embodiment 8, the fourth lens unitG4 comprises solely a bi-convex eighth lens element L8. The eighth lenselement L8 has an aspheric object side surface.

In the zoom lens system according to Embodiment 8, a plane parallelplate P is provided on the object side relative to the image surface S(between the image surface S and the eighth lens element L8).

In the zoom lens system according to Embodiment 8, in zooming from awide-angle limit to a telephoto limit at the time of image taking, thefirst lens unit G1 and the third lens unit G3 move to the object side,the second lens unit G2 moves to the image side with locus of a convexto the image side, and the fourth lens unit G4 moves to the image sidewith locus of a convex to the object side. That is, in zooming, theindividual lens units move along the optical axis such that the intervalbetween the second lens unit G2 and the third lens unit G3 shoulddecrease.

In the zoom lens systems according to Embodiments 1 to 8, the first lensunit G1 comprises two lens elements, the second lens unit G2 comprisestwo lens elements, and the third lens unit G3 comprises three lenselements. Thus, the lens system has a short overall optical length(overall length of lens system).

In the zoom lens systems according to Embodiments 1 to 8, the first lensunit G1, in order from the object side to the image side, is composed ofthe negative meniscus lens element L1 with the convex surface facing theobject side, and the positive lens element L2. These two lens elementsare cemented with each other to constitute a cemented lens element.Thus, a compact lens system is realized. Further, such a constructionpermits favorable compensation of chromatic aberration.

In the zoom lens systems according to Embodiments 1 to 8, in the secondlens unit G2, the third lens element L3, which is an object side lenselement, has an aspheric surface. Therefore, aberrations, particularlydistortion at a wide-angle limit, can be compensated more favorably.Further, in the third lens unit G3, the fifth lens element L5, which isan object side positive lens element, has an aspheric surface.Therefore, aberrations, particularly spherical aberration, can becompensated more favorably.

In the zoom lens systems according to Embodiments 1 to 8, the third lensunit G3 is composed of three lens elements, i.e., in order from theobject side to the image side, the fifth lens element L5 having positiveoptical power, the sixth lens element L6 having negative optical power,and the seventh lens element L7 having positive optical power. The fifthlens element L5, which is an object side positive lens element, and thesixth lens element L6 are cemented with each other to constitute acemented lens element. Therefore, axial aberration, which occurs in thepositive lens element, is compensated in the negative lens element, andthus excellent optical performance is achieved with a small number oflens elements.

In the zoom lens systems according to Embodiments 1 to 8, the fourthlens unit G4 is composed of a single lens element, and the lens elementhas positive optical power. Thus, the lens system has a short overalloptical length (overall length of lens system). Further, at the time offocusing from an infinite-distance object to a close-distance object, asshown in each Fig., the fourth lens unit G4 is drawn out to the objectside so that rapid focusing is achieved easily.

Further, in the zoom lens systems according to Embodiments 1 to 8, inzooming from a wide-angle limit to a telephoto limit at the time ofimage taking, the first lens unit G1, the second lens unit G2, the thirdlens unit G3, and the fourth lens unit G4 are moved individually alongthe optical axis so that zooming is achieved. Then, any lens unit amongthe first lens unit G1, the second lens unit G2, the third lens unit G3and the fourth lens unit G4, or alternatively, a sub lens unitconsisting of a part of a lens unit is moved in a directionperpendicular to the optical axis, so that image point movement causedby vibration of the entire system is compensated, that is, image blurcaused by hand blurring, vibration and the like can be compensatedoptically.

When image point movement caused by vibration of the entire system is tobe compensated, for example, the third lens unit G3 is moved in adirection perpendicular to the optical axis. Thus, image blur iscompensated in a state that size increase in the entire zoom lens systemis suppressed to realize a compact construction and that excellentimaging characteristics such as small decentering coma aberration andsmall decentering astigmatism are maintained.

In a case that a lens unit is composed of a plurality of lens elements,the above-mentioned sub lens unit consisting of a part of a lens unitindicates any one lens element or alternatively a plurality of adjacentlens elements among the plurality of lens elements.

The following description is given for conditions preferred to besatisfied by a zoom lens system like the zoom lens systems according toEmbodiments 1 to 8. Here, a plurality of preferable conditions are setforth for the zoom lens system according to each embodiment. Aconstruction that satisfies all the plural conditions is most desirablefor the zoom lens system. However, when an individual condition issatisfied, a zoom lens system having the corresponding effect isobtained.

In a zoom lens system like the zoom lens systems according toEmbodiments 1 to 8, in order from the object side to the image side,comprising a first lens unit having positive optical power, a secondlens unit having negative optical power, a third lens unit havingpositive optical power, and a fourth lens unit having positive opticalpower, wherein the first lens unit is composed of at most two lenselements, the second lens unit is composed of two lens elements, and thethird lens unit is composed of three lens elements, in order from theobject side to the image side, including an object side lens elementhaving positive optical power, a lens element having negative opticalpower, and an image side lens element having positive optical power(this lens configuration is referred to as basic configuration of theembodiments, hereinafter), the following conditions (b-1) and (a-2) aresatisfied.f _(T) /f _(W)>6.0  (b-1)ω_(W)≧30  (a-2)

where,

f_(T) is a focal length of the entire system at a telephoto limit,

f_(W) is a focal length of the entire system at a wide-angle limit, and

ω_(W) is a half view angle (°) at a wide-angle limit.

In a zoom lens system having the basic configuration like the zoom lenssystems according to Embodiments 1 to 8, it is preferable that thefollowing condition (2-2) is satisfied.−2.0<f ₂ /f _(W)<−1.1  (2-2)

where,

f₂ is a composite focal length of the second lens unit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (2-2) sets forth a suitable focal length of the secondlens unit. When the value exceeds the upper limit of the condition(2-2), the focal length of the second lens unit becomes excessivelylong, and the amount of movement of the second lens unit increases inzooming, which might result in difficulty in achieving a compact zoomlens system having a zooming ratio exceeding 6.0. On the other hand,when the value goes below the lower limit of the condition (2-2), thefocal length of the second lens unit becomes excessively short, whichmight result in difficulty in compensating variation in aberrationcaused by movement of the second lens unit.

When at least one of the following conditions (2-2)′ and (2-2)″ issatisfied, the above-mentioned effect is achieved more successfully.−1.7<f ₂ /f _(W)  (2-2)′f ₂ /f _(W)<−1.5  (2-2)″

In a zoom lens system having the basic configuration like the zoom lenssystems according to Embodiments 1 to 8, it is preferable that thefollowing condition (3-2) is satisfied.1.1<(β_(2T)/β_(2W))/β_(3T)/β_(3W))<5.2  (3-2)

where,

β_(2T) is a lateral magnification of the second lens unit at a telephotolimit,

β_(2W) is a lateral magnification of the second lens unit at awide-angle limit,

β_(3T) is a lateral magnification of the third lens unit at a telephotolimit, and

β_(3W) is a lateral magnification of the third lens unit at a wide-anglelimit.

The condition (3-2) sets forth the ratio between lateral magnificationchange in the second lens unit and lateral magnification change in thethird lens unit. When the value exceeds the upper limit of the condition(3-2), variable magnification load to the second lens unit becomesexcessively great, which might result in difficulty in suppressingoccurrence of aberration due to increase in the power, particularly,occurrence of abaxial aberration such as curvature of field at atelephoto limit or magnification chromatic aberration. On the otherhand, when the value goes below the lower limit of the condition (3-2),it might be difficult to suppress increase in the size of the lenssystem due to increase in the amount of movement of the third lens unit,and occurrence of aberration due to increase in the power of the thirdlens unit, particularly, occurrence of axial aberration such asspherical aberration at a telephoto limit.

When at least one of the following conditions (3-2)′ and (3-2)″ issatisfied, the above-mentioned effect is achieved more successfully.1.5<(β_(2T)/β_(2W))/(β_(3T)/β_(3W))  (3-2)′(β_(2T)/β_(2W))/(β_(3T)/β_(3W))<4.5  (3-2)″

In a zoom lens system having the basic configuration like the zoom lenssystems according to Embodiments 1 to 8, it is preferable that thefollowing condition (4-2) is satisfied.0.9<M ₁ /M ₃<3.0  (4-2)

where,

M₁ is an amount of movement of the first lens unit in the directionalong the optical axis during zooming from a wide-angle limit to atelephoto limit (movement from the image side to the object side ispositive), and

M₃ is an amount of movement of the third lens unit in the directionalong the optical axis during zooming from a wide-angle limit to atelephoto limit (movement from the image side to the object side ispositive).

The condition (4-2) sets forth the ratio between the amount of movementof the first lens unit in the direction along the optical axis and theamount of movement of the third lens unit in the direction along theoptical axis. When the value exceeds the upper limit of the condition(4-2), the amount of movement of the first lens unit increases and then,the overall optical length increases. As a result, a lens barrel at thetime of retraction increases in size, which might result in difficultyin achieving a compact zoom lens system. On the other hand, when thevalue goes below the lower limit of the condition (4-2), the amount ofmovement of the third lens unit becomes excessively great, which mightresult in difficulty in compensating curvature of field or magnificationchromatic aberration.

When at least one of the following conditions (4-2)′ and (4-2)″ issatisfied, the above-mentioned effect is achieved more successfully.1.1<M ₁ /M ₃  (4-2)′M ₁ /M ₃<2.8  (4-2)″

In a zoom lens system having the basic configuration like the zoom lenssystems according to Embodiments 1 to 8, in which the second lens unitincludes a lens element having positive optical power, it is preferablethat the following condition (5) is satisfied.1.88<nd_(2p)<2.20  (5)

where,

nd_(2p) is a refractive index to the d-line of the lens element havingpositive optical power, which is included in the second lens unit.

The condition (5) sets forth the refractive index of the lens elementhaving positive optical power, which is included in the second lensunit. When the value exceeds the upper limit of the condition (5), itmight be difficult to realize mass production of the lens material. Onthe other hand, when the value goes below the lower limit of thecondition (5), it might be difficult to compensate curvature of fieldand distortion at a wide-angle limit, and coma aberration in the entirezooming range from a wide-angle limit to a telephoto limit.

When at least one of the following conditions (5)′ and (5)″ issatisfied, the above-mentioned effect is achieved more successfully.1.90<nd_(2p)  (5)′nd_(2p)<2.15  (5)″

In a zoom lens system having the basic configuration like the zoom lenssystems according to Embodiments 1 to 8, in which the second lens unitincludes a lens element having negative optical power, it is preferablethat the following condition (6) is satisfied.0.35<(r _(2na) +r _(2nb))/(r _(2na) −r _(2nb))<1.20  (6)

where,

r_(2na) is a radius of curvature of an object side surface of the lenselement having negative optical power, which is included in the secondlens unit, and

r_(2nb) is a radius of curvature of an image side surface of the lenselement having negative optical power, which is included in the secondlens unit.

The condition (6) sets forth the shape factor of the lens element havingnegative optical power, which is included in the second lens unit. Whenthe value exceeds the upper limit of the condition (6), it might bedifficult to compensate curvature of field and distortion at awide-angle limit. On the other hand, when the value goes below the lowerlimit of the condition (6), it might be difficult to compensate comaaberration in the entire zooming range from a wide-angle limit to atelephoto limit.

When at least one of the following conditions (6)′ and (6)″ issatisfied, the above-mentioned effect is achieved more successfully.0.60<(r _(2na) +r _(2nb))/(r _(2na) −r _(2nb))  (6)′(r _(2na) +r _(2nb))/(r _(2na) −r _(2nb))<0.90  (6)″

In a zoom lens system having the basic configuration like the zoom lenssystems according to Embodiments 1 to 8, in which the second lens iscomposed of two lens elements, i.e., in order from the object side tothe image side, a lens element having negative optical power and a lenselement having positive optical power, it is preferable that thefollowing condition (7) is satisfied.−8.5<(r _(2nb) +r _(2pa))/(r _(2nb) −r _(2pa))<−3.5  (7)

where,

r_(2nb) is a radius of curvature of an image side surface of the lenselement having negative optical power, which is included in the secondlens unit, and

r_(2pa) is a radius of curvature of an object side surface of the lenselement having positive optical power, which is included in the secondlens unit.

The condition (7) sets forth the shape factor of an air lens between thetwo lens elements constituting the second lens unit. When the valueexceeds the upper limit of the condition (7), it might be difficult tocompensate curvature of field and distortion at a wide-angle limit. Onthe other hand, when the value goes below the lower limit of thecondition (7), it might be difficult to compensate coma aberration inthe entire zooming range from a wide-angle limit to a telephoto limit.

When at least one of the following conditions (7)′ and (7)″ issatisfied, the above-mentioned effect is achieved more successfully.−8.0<(r _(2nb) +r _(2pa))/(r _(2nb) −r _(2pa))  (7)′(r _(2nb) +r _(2pa))/(r _(2nb) −r _(2pa))<−5.2  (7)″

In a zoom lens system having the basic configuration like the zoom lenssystems according to Embodiments 1 to 8, in which the first lens unitincludes a lens element having positive optical power, it is preferablethat the following condition (8) is satisfied.−1.80<(r _(1pa) +r _(1pb))/(r _(1pa) −r _(1pb))<0.00  (8)

where,

r_(1pa) is a radius of curvature of an object side surface of the lenselement having positive optical power, which is included in the firstlens unit, and

r_(1pb) is a radius of curvature of an image side surface of the lenselement having positive optical power, which is included in the firstlens unit.

The condition (8) sets forth the shape factor of the lens element havingpositive optical power, which is included in the first lens unit. Whenthe value exceeds the upper limit of the condition (8), it might bedifficult to compensate coma aberration at a telephoto limit. On theother hand, when the value goes below the lower limit of the condition(8), it might be difficult to compensate curvature of field at awide-angle limit.

When at least one of the following conditions (8)′ and (8)″ issatisfied, the above-mentioned effect is achieved more successfully.−1.47<(r _(1pa) +r _(1pb))/(r _(1pa) −r _(1pb))  (8)′(r _(1pa) +r _(1pb))/(r _(1pa) −r _(1pb))<−1.20  (8)″

In a zoom lens system having the basic configuration like the zoom lenssystems according to Embodiments 1 to 8, it is preferable that thefollowing condition (9) is satisfied.1.87<f ₃ /f _(W)<3.00  (9)

where,

f₃ is a composite focal length of the third lens unit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (9) sets forth a suitable focal length of the third lensunit. When the value exceeds the upper limit of the condition (9), thefocal length of the third lens unit becomes excessively long, whichmight result in difficulty in achieving a compact zoom lens system.Further, when the value exceeds the upper limit of the condition (9),the amount of movement of, for example, the third lens unit becomesexcessively great when the third lens unit is moved in a directionperpendicular to the optical axis for blur compensation. Such asituation is not desirable. On the other hand, when the value goes belowthe lower limit of the condition (9), the focal length of the third lensunit becomes excessively short. Then, the aberration compensationcapability of the third lens unit becomes excessively high, andcompensation of various aberrations is not well-balanced, which mightresult in difficulty in achieving a compact zoom lens system.

When at least one of the following conditions (9)′ and (9)″ issatisfied, the above-mentioned effect is achieved more successfully.1.90<f ₃ /f _(W)  (9)′f ₃ /f _(W)<2.06  (9)″

In a zoom lens system having the basic configuration like the zoom lenssystems according to Embodiments 1 to 8, it is preferable that thefollowing condition (10) is satisfied.0.5<f _(3IL) /f ₃<1.5  (10)

where,

f_(3IL) is a focal length of the image side lens element having positiveoptical power, which is included in the third lens unit, and

f₃ is a composite focal length of the third lens unit.

The condition (10) sets forth a suitable focal length of the image sidelens element having positive optical power, which is included in thethird lens unit. When the value exceeds the upper limit of the condition(10), it might be difficult to compensate spherical aberration and comaaberration in a balanced manner by other lens elements, although theoverall optical length can be reduced. On the other hand, when the valuegoes below the lower limit of the condition (10), it might be difficultto reduce the overall optical length, although spherical aberration andcoma aberration can be compensated in a balanced manner by other lenselements.

When at least one of the following conditions (10)′ and (10)″ issatisfied, the above-mentioned effect is achieved more successfully.1.0<f _(3IL) /f ₃  (10)′f _(IL) /f ₃<1.3  (10)″

In a zoom lens system having the basic configuration like the zoom lenssystems according to Embodiments 1 to 8, it is preferable that thefollowing condition (11) is satisfied.−1.00<f _(3n) /f ₃<−0.25  (11)

where,

f_(3n) is a focal length of the lens element having negative opticalpower, which is included in the third lens unit, and

f₃ is a composite focal length of the third lens unit.

The condition (11) sets forth a suitable focal length of the lenselement having negative optical power, which is included in the thirdlens unit. When the value exceeds the upper limit of the condition (11),it might be difficult to compensate spherical aberration and comaaberration in a balanced manner by other lens elements, although theoverall optical length can be reduced. On the other hand, when the valuegoes below the lower limit of the condition (11), it might be difficultto reduce the overall optical length, although spherical aberration andcoma aberration can be compensated in a balanced manner by other lenselements.

When at least one of the following conditions (11)′ and (11)″ issatisfied, the above-mentioned effect is achieved more successfully.−0.68<f _(3n) /f ₃  (11)′f _(3n) /f ₃<−0.46  (11)″

Each of the lens units constituting the zoom lens system according toany of Embodiments 1 to 8 is composed exclusively of refractive typelens elements that deflect the incident light by refraction (that is,lens elements of a type in which deflection is achieved at the interfacebetween media each having a distinct refractive index). However, thepresent invention is not limited to this. For example, the lens unitsmay employ diffractive type lens elements that deflect the incidentlight by diffraction; refractive-diffractive hybrid type lens elementsthat deflect the incident light by a combination of diffraction andrefraction; or gradient index type lens elements that deflect theincident light by distribution of refractive index in the medium. Inparticular, in the refractive-diffractive hybrid type lens elements,when a diffraction structure is formed in the interface between mediahaving mutually different refractive indices, wavelength dependence inthe diffraction efficiency is improved. Thus, such a configuration ispreferable.

Moreover, in each embodiment, a configuration has been described that onthe object side relative to the image surface S (that is, between theimage surface S and the most image side lens surface of the fourth lensunit G4), a plane parallel plate P such as an optical low-pass filterand a face plate of an image sensor is provided. This low-pass filtermay be: a birefringent type low-pass filter made of, for example, acrystal whose predetermined crystal orientation is adjusted; or a phasetype low-pass filter that achieves required characteristics of opticalcut-off frequency by diffraction.

Embodiment 9

FIG. 20 is a schematic construction diagram of a digital still cameraaccording to Embodiment 9. In FIG. 20, the digital still cameracomprises: an imaging device having a zoom lens system 1 and an imagesensor 2 composed of a CCD; a liquid crystal display monitor 3; and abody 4. The employed zoom lens system 1 is a zoom lens system accordingto Embodiment 1. In FIG. 20, the zoom lens system 1 comprises a firstlens unit G1, a second lens unit G2, an aperture diaphragm A, a thirdlens unit G3, and a fourth lens unit G4. In the body 4, the zoom lenssystem 1 is arranged on the front side, and the image sensor 2 isarranged on the rear side of the zoom lens system 1. On the rear side ofthe body 4, the liquid crystal display monitor 3 is arranged, and anoptical image of a photographic object generated by the zoom lens system1 is formed on an image surface S.

A lens barrel comprises a main barrel 5, a moving barrel 6 and acylindrical cam 7. When the cylindrical cam 7 is rotated, the first lensunit G1, the second lens unit G2, the aperture diaphragm A and the thirdlens unit G3, and the fourth lens unit G4 move to predeterminedpositions relative to the image sensor 2, so that zooming from awide-angle limit to a telephoto limit is achieved. The fourth lens unitG4 is movable in an optical axis direction by a motor for focusadjustment.

In this way, when the zoom lens system according to Embodiment 1 isemployed in a digital still camera, a small digital still camera isobtained that has a high resolution and high capability of compensatingthe curvature of field and that has a short overall length of lenssystem at the time of non-use. Here, in the digital still camera shownin FIG. 20, any one of the zoom lens systems according to Embodiments 2to 8 may be employed in place of the zoom lens system according toEmbodiment 1. Further, the optical system of the digital still camerashown in FIG. 20 is applicable also to a digital video camera for movingimages. In this case, moving images with high resolution can be acquiredin addition to still images.

Here, the digital still camera according to Embodiment 9 has beendescribed for a case that the employed zoom lens system 1 is a zoom lenssystem according to any of Embodiments 1 to 8. However, in these zoomlens systems, the entire zooming range need not be used. That is, inaccordance with a desired zooming range, a range where satisfactoryoptical performance is obtained may exclusively be used. Then, the zoomlens system may be used as one having a lower magnification than thezoom lens systems described in Embodiments 1 to 8.

Further, Embodiment 9 has been described for a case that the zoom lenssystem is applied to a lens barrel of so-called barrel retractionconstruction. However, the present invention is not limited to this. Forexample, the zoom lens system may be applied to a lens barrel ofso-called bending construction where a prism having an internalreflective surface or a front surface reflective minor is arranged at anarbitrary position within the first lens unit G1 or the like. Further,in Embodiment 9, the zoom lens system may be applied to a so-calledsliding lens barrel in which a part of the lens units constituting thezoom lens system like the entirety of the second lens unit G2, theentirety of the third lens unit G3, or alternatively a part of thesecond lens unit G2 or the third lens unit G3 is caused to escape fromthe optical axis at the time of retraction.

Further, an imaging device comprising a zoom lens system according toany of Embodiments 1 to 8 described above and an image sensor such as aCCD or a CMOS may be applied to a mobile telephone, a PDA (PersonalDigital Assistance), a surveillance camera in a surveillance system, aWeb camera, a vehicle-mounted camera or the like.

Numerical examples are described below in which the zoom lens systemsaccording to Embodiments 1 to 8 are implemented. Here, in the numericalexamples, the units of length are all “mm”, while the units of viewangle are all “°”. Moreover, in the numerical examples, r is the radiusof curvature, d is the axial distance, nd is the refractive index to thed-line, and vd is the Abbe number to the d-line. In the numericalexamples, the surfaces marked with * are aspherical surfaces, and theaspherical surface configuration is defined by the following expression.

$Z = {\frac{h^{2}/r}{1 + \sqrt{1 - {\left( {1 + \kappa} \right)\left( {h/r} \right)^{2}}}} + {A\; 4\; h^{4}} + {A\; 6\; h^{6}} + {A\; 8\; h^{8}} + {A\; 10\; h^{10}}}$

Here, K is the conic constant, A4, A6, A8 and A10 are a fourth-order,sixth-order, eighth-order and tenth-order aspherical coefficients,respectively.

FIGS. 2, 5, 7, 10, 12, 15, 17 and 19 are longitudinal aberrationdiagrams of the zoom lens systems according to Embodiments 1 to 8,respectively.

In each longitudinal aberration diagram, part (a) shows the aberrationat a wide-angle limit, part (b) shows the aberration at a middleposition, and part (c) shows the aberration at a telephoto limit. Eachlongitudinal aberration diagram, in order from the left-hand side, showsthe spherical aberration (SA (mm)), the astigmatism (AST (mm)) and thedistortion (DIS (%)). In each spherical aberration diagram, the verticalaxis indicates the F-number (in each Fig., indicated as F), and thesolid line, the short dash line and the long dash line indicate thecharacteristics to the d-line, the F-line and the C-line, respectively.In each astigmatism diagram, the vertical axis indicates the imageheight (in each Fig., indicated as H), and the solid line and the dashline indicate the characteristics to the sagittal plane (in each Fig.,indicated as “s”) and the meridional plane (in each Fig., indicated as“m”), respectively. In each distortion diagram, the vertical axisindicates the image height (in each Fig., indicated as H).

FIGS. 3, 8 and 13 are lateral aberration diagrams of the zoom lenssystems at a telephoto limit according to Embodiments 1, 3 and 5,respectively.

In each lateral aberration diagram, the aberration diagrams in the upperthree parts correspond to a basic state where image blur compensation isnot performed at a telephoto limit, while the aberration diagrams in thelower three parts correspond to an image blur compensation state wherethe entirety of the third lens unit G3 is moved by a predeterminedamount in a direction perpendicular to the optical axis at a telephotolimit. Among the lateral aberration diagrams of a basic state, the upperpart shows the lateral aberration at an image point of 70% of themaximum image height, the middle part shows the lateral aberration atthe axial image point, and the lower part shows the lateral aberrationat an image point of −70% of the maximum image height. Among the lateralaberration diagrams of an image blur compensation state, the upper partshows the lateral aberration at an image point of 70% of the maximumimage height, the middle part shows the lateral aberration at the axialimage point, and the lower part shows the lateral aberration at an imagepoint of −70% of the maximum image height. In each lateral aberrationdiagram, the horizontal axis indicates the distance from the principalray on the pupil surface, and the solid line, the short dash line andthe long dash line indicate the characteristics to the d-line, theF-line and the C-line, respectively. In each lateral aberration diagram,the meridional plane is adopted as the plane containing the optical axisof the first lens unit G1 and the optical axis of the third lens unitG3.

Here, in the zoom lens system according to each example, the amount ofmovement of the third lens unit G3 in a direction perpendicular to theoptical axis in the image blur compensation state at a telephoto limitis as follows.

Amount of movement Example (mm) 1 0.131 3 0.129 5 0.164

Here, when the shooting distance is infinity, at a telephoto limit, theamount of image decentering in a case that the zoom lens system inclinesby 0.3° is equal to the amount of image decentering in a case that theentirety of the third lens unit G3 displaces in parallel by each of theabove-mentioned values in a direction perpendicular to the optical axis.

As seen from the lateral aberration diagrams, satisfactory symmetry isobtained in the lateral aberration at the axial image point. Further,when the lateral aberration at the +70% image point and the lateralaberration at the −70% image point are compared with each other in thebasic state, all have a small degree of curvature and almost the sameinclination in the aberration curve. Thus, decentering coma aberrationand decentering astigmatism are small. This indicates that sufficientimaging performance is obtained even in the image blur compensationstate. Further, when the image blur compensation angle of a zoom lenssystem is the same, the amount of parallel translation required forimage blur compensation decreases with decreasing focal length of theentire zoom lens system. Thus, at arbitrary zoom positions, sufficientimage blur compensation can be performed for image blur compensationangles up to 0.3° without degrading the imaging characteristics.

Numerical Example 1

The zoom lens system of Numerical Example 1 corresponds to Embodiment 1shown in FIG. 1. Table 1 shows the surface data of the zoom lens systemof Numerical Example 1. Table 2 shows the aspherical data. Table 3 showsvarious data.

TABLE 1 (Surface data) Surface number r d nd vd Object surface ∞  123.27352 0.80000 1.84666 23.8  2 16.49277 3.20000 1.72916 54.7  3117.70340 Variable  4* −551.78280 1.20000 1.85976 40.6  5* 5.897161.94000  6 8.72337 1.70000 1.94595 18.0  7 14.57504 Variable  8 ∞0.00000 (Diaphragm)  9* 4.53459 2.50000 1.77377 47.2 10 15.97304 0.400001.80518 25.5 11 3.86773 0.50000 12 11.87353 1.80000 1.72916 54.7 13−75.00131 Variable  14* 14.48408 1.80000 1.58913 61.3 15 −104.90850Variable 16 ∞ 1.00000 1.51680 64.2 17 ∞ (BF) Image surface ∞

TABLE 2 (Aspherical data) Surface No. 4 K = 0.00000E+00, A4 =6.35805E−06, A6 = 3.23164E−07, A8 = 0.00000E+00 A10 = 0.00000E+00Surface No. 5 K = −2.54216E+00, A4 = 1.28993E−03, A6 = −1.61960E−05, A8= 3.66074E−07 A10 = −1.38864E−09 Surface No. 9 K = −3.78055E−01, A4 =5.10493E−05, A6 = 1.60037E−05, A8 = −2.91615E−06 A10 = 2.64245E−07Surface No. 14 K = 0.00000E+00, A4 = 2.84410E−05, A6 = 1.40555E−06, A8 =−3.29006E−08 A10 = 0.00000E+00

TABLE 3 (Various data) Zooming ratio 6.54005 Wide-angle Middle Telephotolimit position limit Focal length 6.7966 14.4264 44.4500 F-number3.37524 3.90094 6.26203 View angle 30.8736 14.9460 4.8778 Image height3.8300 3.8300 3.8300 Overall length 44.7962 45.7623 60.0080 of lenssystem BF 0.49778 0.51223 0.49656 d3 0.6000 8.6030 17.7617 d7 17.26047.1565 1.3000 d13 2.4311 3.7617 20.6110 d15 7.1669 8.8889 2.9987Entrance pupil 13.8997 27.8899 55.2641 position Exit pupil −16.4101−20.7719 244.3409 position Front principal 17.9642 32.5381 107.8169points position Back principal 37.9996 31.3359 15.5580 points positionSingle lens data Lens Initial surface Focal element number length 1 1−70.6835 2 2 25.9586 3 4 −6.7798 4 6 20.1269 5 9 7.4713 6 10 −6.4331 712 14.1822 8 14 21.7244 Zoom lens unit data Initial Overall Lens surfaceFocal length of Front principal Back principal unit No. length lens unitpoints position points position 1 1 42.36214 4.00000 −0.73159 1.03016 24 −10.88041 4.84000 0.20227 1.64041 3 8 13.92259 5.20000 −2.241970.21723 4 14 21.72442 1.80000 0.13819 0.79912 Magnification of zoom lensunit Lens Initial Wide-angle Middle Telephoto unit surface No. limitposition limit 1 1 0.00000 0.00000 0.00000 2 4 −0.39266 −0.55212−1.03152 3 8 −0.71588 −1.25665 −1.33373 4 14 0.57077 0.49084 0.76269

Numerical Example 2

The zoom lens system of Numerical Example 2 corresponds to Embodiment 2shown in FIG. 4. Table 4 shows the surface data of the zoom lens systemof Numerical Example 2. Table 5 shows the aspherical data. Table 6 showsvarious data.

TABLE 4 (Surface data) Surface number r d nd vd Object surface ∞  121.67895 0.80000 2.00170 20.6  2 16.21267 3.20000 1.72916 54.7  3174.74440 Variable  4* −53.85976 1.10000 1.85976 40.6  5* 5.719970.92630  6 7.76084 1.70000 2.00170 20.6  7 16.00169 Variable  8 ∞0.00000 (Diaphragm)  9* 4.28080 2.50000 1.85135 40.1 10 7.80657 0.400002.00170 20.6 11 3.57214 0.50000 12 9.44005 1.50000 1.77250 49.6 13214.22130 Variable  14* 12.42141 1.80000 1.62299 58.1 15 −75.23346Variable 16 ∞ 1.00000 1.51680 64.2 17 ∞ (BF) Image surface ∞

TABLE 5 (Aspherical data) Surface No. 4 K = 0.00000E+00, A4 =4.56239E−05, A6 = −6.94009E−07, A8 = 1.81220E−08 A10 = −8.02787E−11Surface No. 5 K = −1.98341E+00, A4 = 1.07747E−03, A6 = −7.31374E−06, A8= 1.86112E−07 A10 = 5.59108E−10 Surface No. 9 K = −3.53088E−01, A4 =4.87967E−05, A6 = 2.95696E−05, A8 = −7.13705E−06 A10 = 7.21043E−07Surface No. 14 K = 0.00000E+00, A4 = 6.02721E−05, A6 = 2.35414E−06, A8 =−1.45477E−07 A10 = 3.81222E−09

TABLE 6 (Various data) Zooming ratio 6.58661 Wide-angle Middle Telephotolimit position limit Focal length 7.0002 17.9935 46.1078 F-number3.42534 4.28755 5.96646 View angle 31.0628 12.2142 4.6470 Image height3.8300 3.8300 3.8300 Overall length 41.8456 38.5980 53.0305 of lenssystem BF 0.50774 0.54740 0.50181 d3 0.6000 6.5818 17.3687 d7 16.64662.8215 1.0000 d13 2.3747 3.4807 17.1718 d15 6.2903 9.7403 1.5619Entrance pupil 14.0988 19.1342 55.2858 position Exit pupil −15.3366−21.2790 122.6438 position Front principal 18.0062 22.2940 118.7990points position Back principal 34.8454 20.6045 6.9227 points positionSingle lens data Lens Initial surface Focal element number length 1 1−69.2618 2 2 24.3018 3 4 −5.9634 4 6 13.6363 5 9 8.3957 6 10 −6.9006 712 12.7428 8 14 17.2488 Zoom lens unit data Initial Overall Lens surfaceFocal length of Front principal Back principal unit No. length lens unitpoints position points position 1 1 38.69978 4.00000 −0.62539 1.15784 24 −10.96627 3.72630 0.32297 1.75775 3 8 13.67425 4.90000 −3.21446−0.36143 4 14 17.24879 1.80000 0.15841 0.84054 Magnification of zoomlens unit Lens Initial Wide-angle Middle Telephoto unit surface No.limit position limit 1 1 0.00000 0.00000 0.00000 2 4 −0.45753 −0.60969−1.52316 3 8 −0.77212 −2.46223 −0.99453 4 14 0.51204 0.30972 0.78651

Numerical Example 3

The zoom lens system of Numerical Example 3 corresponds to Embodiment 3shown in FIG. 6. Table 7 shows the surface data of the zoom lens systemof Numerical Example 3. Table 8 shows the aspherical data. Table 9 showsvarious data.

TABLE 7 (Surface data) Surface number r d nd vd Object surface ∞  120.56187 0.80000 1.92286 20.9  2 14.81270 3.20000 1.72916 54.7  3158.73300 Variable  4* −59.17839 1.10000 1.85976 40.6  5* 5.511371.13160  6 7.62681 1.70000 1.94595 18.0  7 14.57504 Variable  8 ∞0.00000 (Diaphragm)  9* 4.20287 2.50000 1.85135 40.1 10 9.49076 0.400001.92286 20.9 11 3.47256 0.50000 12 9.45232 1.50000 1.77250 49.6 13−630.07970 Variable  14* 12.45881 1.80000 1.62299 58.1 15 −53.07139Variable 16 ∞ 1.00000 1.51680 64.2 17 ∞ (BF) Image surface ∞

TABLE 8 (Aspherical data) Surface No. 4 K = 0.00000E+00, A4 =7.16481E−05, A6 = −9.20654E−07, A8 = 9.31422E−09 A10 = −1.08989E−11Surface No. 5 K = −1.96424E+00, A4 = 1.20304E−03, A6 = −7.06323E−06, A8= 1.22887E−07 A10 = 1.45469E−09 Surface No. 9 K = −4.49892E−01, A4 =1.71358E−04, A6 = 2.95164E−05, A8 = −5.81944E−06 A10 = 6.34879E−07Surface No. 14 K = 0.00000E+00, A4 = 3.68685E−05, A6 = 7.24260E−06, A8 =−3.15541E−07 A10 = 5.13901E−09

TABLE 9 (Various data) Zooming ratio 6.52948 Wide-angle Middle Telephotolimit position limit Focal length 6.1187 12.9818 39.9518 F-number3.12003 3.77592 5.46453 View angle 34.8394 16.8681 5.3822 Image height3.8300 3.8300 3.8300 Overall length 40.0820 35.9984 50.0898 of lenssystem BF 0.50106 0.53718 0.50627 d3 0.6000 4.1205 15.5150 d7 15.72904.5669 1.0000 d13 2.2919 3.2444 15.6615 d15 5.3284 7.8978 1.7755Entrance pupil 13.4079 15.7987 50.2041 position Exit pupil −14.5439−19.3553 134.0690 position Front principal 17.0381 20.3085 102.1063points position Back principal 33.9633 23.0165 10.1380 points positionSingle lens data Lens Initial surface Focal element number length 1 1−61.5140 2 2 22.1975 3 4 −5.8185 4 6 15.1150 5 9 7.2781 6 10 −6.1295 712 12.0675 8 14 16.3687 Zoom lens unit data Initial Overall Lens surfaceFocal length of Front principal Back principal unit No. length lens unitpoints position points position 1 1 35.95275 4.00000 −0.57161 1.19624 24 −9.80239 3.93160 0.32635 1.74700 3 8 12.20044 4.90000 −2.62124 0.034604 14 16.36872 1.80000 0.21311 0.89223 Magnification of zoom lens unitLens Initial Wide-angle Middle Telephoto unit surface No. limit positionlimit 1 1 0.00000 0.00000 0.00000 2 4 −0.43721 −0.51865 −1.30606 3 8−0.71015 −1.78990 −1.11238 4 14 0.54813 0.38896 0.76487

Numerical Example 4

The zoom lens system of Numerical Example 4 corresponds to Embodiment 4shown in FIG. 9. Table 10 shows the surface data of the zoom lens systemof Numerical Example 4. Table 11 shows the aspherical data. Table 12shows various data.

TABLE 10 (Surface data) Surface number r d nd vd Object surface ∞  122.98440 0.80000 2.00170 20.6  2 17.06934 3.00000 1.80420 46.5  388.78142 Variable  4* −221.40520 1.00000 1.85976 40.6  5* 5.565271.39220  6 8.04492 1.70000 2.00170 20.6  7 14.35270 Variable  8(Diaphragm) ∞ 0.00000  9* 4.58023 2.50000 1.77377 47.2 10 13.170910.40000 1.84666 23.8 11 3.98157 0.50000 12 11.32115 1.50000 1.80420 46.513 −172.13620 Variable 14* 15.84590 1.80000 1.80420 46.5 15 696.20750Variable 16 ∞ 1.00000 1.51680 64.2 17 ∞ (BF) Image surface ∞

TABLE 11 (Aspherical data) Surface No. 4 K = 0.00000E+00, A4 =−7.92798E−05, A6 = 1.31994E−06, A8 = 0.00000E+00 A10 = 0.00000E+00Surface No. 5 K = −1.64472E+00, A4 = 8.04967E−04, A6 = −4.09967E−06, A8= 9.96207E−08 A10 = 3.79729E−09 Surface No. 9 K = −3.85474E−01, A4 =7.27041E−05, A6 = 1.43854E−05, A8 = −3.37492E−06 A10 = 3.29500E−07Surface No. 14 K = 0.00000E+00, A4 = 4.52987E−05, A6 = 3.58657E−07, A8 =0.00000E+00 A10 = 0.00000E+00

TABLE 12 (Various data) Zooming ratio 6.54358 Wide-angle MiddleTelephoto limit position limit Focal length 6.7963 17.3331 44.4720F-number 3.43627 3.88419 5.87738 View angle 32.0601 12.5864 4.8709 Imageheight 3.8300 3.8300 3.8300 Overall length 44.4426 45.4138 57.7571 oflens system BF 0.49855 0.53779 0.50695 d3 0.5000 11.3199 18.7857 d717.5535 5.3040 1.4500 d13 3.9343 3.8667 18.8854 d15 6.3640 8.7933 2.5369Entrance pupil 13.4475 33.8815 59.9670 position Exit pupil −18.1536−20.4311 278.7394 position Front principal 17.7674 36.8869 111.5473points position Back principal 37.6463 28.0807 13.2851 points positionSingle lens data Lens Initial surface Focal element number length 1 1−71.0212 2 2 25.7964 3 4 −6.3015 4 6 16.1025 5 9 8.0531 6 10 −6.8775 712 13.2571 8 14 20.1391 Zoom lens unit data Overall Initial length ofLens surface Focal lens Front principal Back principal unit No. lengthunit points position points position 1 1 42.02118 3.80000 −0.982290.81730 2 4 −10.85227 4.09220 0.21956 1.61285 3 8 13.70595 4.90000−2.18526 0.19508 4 14 20.13910 1.80000 −0.02321 0.78029 Magnification ofzoom lens unit Lens Initial Wide-angle Middle Telephoto unit surface No.limit position limit 1 1 0.00000 0.00000 0.00000 2 4 −0.39511 −0.65191−1.18204 3 8 −0.71083 −1.39583 −1.16962 4 14 0.57587 0.45330 0.76549

Numerical Example 5

The zoom lens system of Numerical Example 5 corresponds to Embodiment 5shown in FIG. 11. Table 13 shows the surface data of the zoom lenssystem of Numerical Example 5. Table 14 shows the aspherical data. Table15 shows various data.

TABLE 13 (Surface data) Surface number r d nd vd Object surface ∞  123.92026 0.80000 2.00170 20.6  2 17.23850 2.50000 1.80420 46.5  3*91.93466 Variable  4* −86.26322 1.00000 1.85976 40.6  5* 5.30963 1.09570 6 7.43523 1.70000 2.00170 20.6  7 14.35270 Variable  8 (Diaphragm) ∞0.00000  9* 4.78659 2.10000 1.77377 47.2 10 10.28002 0.80000 1.9228620.9 11 4.30394 0.50000 12 11.80608 1.50000 1.80420 46.5 13 −41.97623Variable 14* 18.23360 1.80000 1.80420 46.5 15 449.20610 Variable 16 ∞1.00000 1.51680 64.2 17 ∞ (BF) Image surface ∞

TABLE 14 (Aspherical data) Surface No. 3 K = 0.00000E+00, A4 =1.16573E−06, A6 = 3.73564E−10, A8 = 0.00000E+00 A10 = 0.00000E+00Surface No. 4 K = 0.00000E+00, A4 = 4.11218E−05, A6 = 4.14113E−07, A8 =0.00000E+00 A10 = 0.00000E+00 Surface No. 5 K = −2.55557E+00, A4 =1.78988E−03, A6 = −2.05242E−05, A8 = 4.89013E−07 A10 = 9.76558E−10Surface No. 9 K = −4.57612E−01, A4 = 8.64666E−05, A6 = 3.31418E−05, A8 =−6.94709E−06 A10 = 6.20715E−07 Surface No. 14 K = 0.00000E+00, A4 =3.07143E−05, A6 = 2.65662E−06, A8 = 0.00000E+00 A10 = 0.00000E+00

TABLE 15 (Various data) Zooming ratio 6.54154 Wide-angle MiddleTelephoto limit position limit Focal length 6.7983 17.3298 44.4713F-number 3.35579 3.99862 4.53813 View angle 32.0536 12.6171 4.8991 Imageheight 3.8300 3.8300 3.8300 Overall length 40.9465 44.9233 56.8471 oflens system BF 0.50091 0.52914 0.50678 d3 0.6000 11.6273 24.8265 d715.2623 4.7479 1.4500 d13 2.5571 3.4896 12.7618 d15 7.2306 9.7337 2.5063Entrance pupil 12.0260 31.2012 94.2363 position Exit pupil −15.9753−20.1365 −50.5394 position Front principal 16.0192 33.9985 99.9644points position Back principal 34.1483 27.5935 12.3759 points positionSingle lens data Lens Initial surface Focal element number length 1 1−65.5343 2 2 25.9947 3 4 −5.7884 4 6 13.7142 5 9 9.9217 6 10 −8.5733 712 11.6022 8 14 23.5883 Zoom lens unit data Initial Overall Lens surfaceFocal length of Front principal Back principal unit No. length lens unitpoints position points position 1 1 44.68006 3.30000 −0.90484 0.65703 24 −10.42881 3.79570 0.26532 1.66111 3 8 12.81592 4.90000 −1.395790.73000 4 14 23.58831 1.80000 −0.04213 0.76205 Magnification of zoomlens unit Lens Initial Wide-angle Middle Telephoto unit surface No.limit position limit 1 1 0.00000 0.00000 0.00000 2 4 −0.33923 −0.52896−1.60039 3 8 −0.74721 −1.48745 −0.77711 4 14 0.60028 0.49297 0.80031

Numerical Example 6

The zoom lens system of Numerical Example 6 corresponds to Embodiment 6shown in FIG. 14. Table 16 shows the surface data of the zoom lenssystem of Numerical Example 6. Table 17 shows the aspherical data. Table18 shows various data.

TABLE 16 (Surface data) Surface number r d nd vd Object surface ∞  122.01411 0.80000 2.14422 17.5  2 16.76615 2.50000 1.82080 42.7  3*101.42760 Variable  4* −71.58793 1.00000 1.85976 40.6  5* 5.130921.09570  6 7.40182 1.70000 2.00170 20.6  7 14.35270 Variable  8(Diaphragm) ∞ 0.00000  9* 4.80218 2.10000 1.77377 47.2 10 9.875350.80000 1.92286 20.9 11 4.30138 0.50000 12 11.64846 1.50000 1.80420 46.513 −48.27259 Variable 14* 19.51788 1.30000 1.80420 46.5 15 −601.21670Variable 16 ∞ 1.00000 1.51680 64.2 17 ∞ (BF) Image surface ∞

TABLE 17 (Aspherical data) Surface No. 3 K = 0.00000E+00, A4 =1.96399E−06, A6 = 8.38790E−10, A8 = 0.00000E+00 A10 = 0.00000E+00Surface No. 4 K = 0.00000E+00, A4 = 2.08635E−05, A6 = 4.82445E−07, A8 =0.00000E+00 A10 = 0.00000E+00 Surface No. 5 K = −2.72794E+00, A4 =2.05037E−03, A6 = −3.37206E−05, A8 = 8.72404E−07 A10 = −5.23638E−09Surface No. 9 K = −4.61942E−01, A4 = 1.03075E−04, A6 = 2.43831E−05, A8 =−4.51015E−06 A10 = 4.15499E−07 Surface No. 14 K = 0.00000E+00, A4 =2.82102E−05, A6 = 3.05454E−06, A8 = 0.00000E+00 A10 = 0.00000E+00

TABLE 18 (Various data) Zooming ratio 6.54969 Wide-angle MiddleTelephoto limit position limit Focal length 6.7999 17.3217 44.5372F-number 3.42679 4.00985 4.56886 View angle 32.0408 12.5843 4.9066 Imageheight 3.8300 3.8300 3.8300 Overall length 41.1512 44.8950 53.2882 oflens system BF 0.50957 0.51183 0.52021 d3 0.6000 10.9391 21.3625 d715.4165 5.6233 1.3000 d13 2.4448 3.4802 12.6158 d15 7.8846 10.04483.1939 Entrance pupil 11.9887 32.6384 82.8481 position Exit pupil−16.1869 −20.1889 −50.2594 position Front principal 16.0192 35.465988.3232 points position Back principal 34.3513 27.5733 8.7510 pointsposition Single lens data Lens Initial surface Focal element numberlength 1 1 −66.9089 2 2 24.1504 3 4 −5.5354 4 6 13.5941 5 9 10.2331 6 10−8.8686 7 12 11.8005 8 14 23.5288 Zoom lens unit data Initial OverallLens surface Focal length of Front principal Back principal unit No.length lens unit points position points position 1 1 39.22731 3.30000−0.83975 0.75865 2 4 −9.73077 3.79570 0.26561 1.66074 3 8 13.019464.90000 −1.48970 0.66880 4 14 23.52878 1.30000 0.02268 0.60146Magnification of zoom lens unit Lens Initial Wide-angle Middle Telephotounit surface No. limit position limit 1 1 0.00000 0.00000 0.00000 2 4−0.37298 −0.61781 −1.82667 3 8 −0.79375 −1.44795 −0.79235 4 14 0.585530.49362 0.78444

Numerical Example 7

The zoom lens system of Numerical Example 7 corresponds to Embodiment 7shown in FIG. 16. Table 19 shows the surface data of the zoom lenssystem of Numerical Example 7. Table 20 shows the aspherical data. Table21 shows various data.

TABLE 19 (Surface data) Surface number r d nd vd Object surface ∞  124.63915 0.80000 1.92286 20.9  2 17.69162 2.90000 1.77250 49.6  3141.43600 Variable  4* −74.12426 0.95000 1.85976 40.6  5* 5.961721.39660  6 8.26210 1.70000 2.14422 17.5  7 12.83109 Variable  8(Diaphragm) ∞ 0.00000  9* 4.65521 2.50090 1.80139 45.4 10 11.213940.50000 1.92286 20.9 11 4.06867 0.50000 12 11.22865 1.50000 1.80420 46.513 −68.81526 Variable 14* 15.96294 1.70000 1.80610 40.7 15 −270.01270Variable 16 ∞ 1.00000 1.51680 64.2 17 ∞ (BF) Image surface ∞

TABLE 20 (Aspherical data) Surface No. 4 K = 0.00000E+00, A4 =3.83404E−05, A6 = 5.29405E−08, A8 = 1.02032E−09 A10 = 0.00000E+00Surface No. 5 K = −3.21567E+00, A4 = 1.68391E−03, A6 = −3.06050E−05, A8= 7.28861E−07 A10 = −5.38787E−09 Surface No. 9 K = −3.45514E−01, A4 =−2.07950E−05, A6 = 2.45075E−05, A8 = −6.29992E−06 A10 = 6.15382E−07Surface No. 14 K = 0.00000E+00, A4 = 5.07793E−05, A6 = 3.47763E−07, A8 =0.00000E+00 A10 = 0.00000E+00

TABLE 21 (Various data) Zooming ratio 6.54156 Wide-angle MiddleTelephoto limit position limit Focal length 6.4574 16.4623 42.2414F-number 3.43301 3.85000 5.93349 View angle 33.6879 13.1888 5.1236 Imageheight 3.8300 3.8300 3.8300 Overall length 43.0231 45.0104 57.0342 oflens system BF 0.49458 0.54184 0.50628 d3 0.5000 11.6929 18.6778 d716.7547 5.2707 1.4500 d13 3.9231 3.9579 18.3061 d15 5.9032 8.0996 2.6465Entrance pupil 12.9125 34.3781 57.9941 position Exit pupil −18.2489−20.5320 155.8859 position Front principal 17.1452 37.9805 111.7193points position Back principal 36.5657 28.5482 14.7928 points positionSingle lens data Lens Initial surface Focal element number length 1 1−71.9643 2 2 25.9114 3 4 −6.3830 4 6 16.9188 5 9 8.4915 6 10 −7.1597 712 12.1049 8 14 18.7469 Zoom lens unit data Initial Overall Lens surfaceFocal length of Front principal Back principal unit No. length lens unitpoints position points position 1 1 41.71577 3.70000 −0.61640 1.06461 24 −10.48715 4.04660 0.32254 1.79750 3 8 13.07665 5.00090 −1.998390.39268 4 14 18.74694 1.70000 0.05268 0.80892 Magnification of zoom lensunit Lens Initial Wide-angle Middle Telephoto unit surface No. limitposition limit 1 1 0.00000 0.00000 0.00000 2 4 −0.37763 −0.63260−1.09323 3 8 −0.71161 −1.36698 −1.23644 4 14 0.57603 0.45635 0.74913

Numerical Example 8

The zoom lens system of Numerical Example 8 corresponds to Embodiment 8shown in FIG. 18. Table 22 shows the surface data of the zoom lenssystem of Numerical Example 8. Table 23 shows the aspherical data. Table24 shows various data.

TABLE 22 (Surface data) Surface number r d nd vd Object surface ∞  125.31776 0.80000 1.92286 20.9  2 18.23858 2.90000 1.77250 49.6  3141.43600 Variable  4* −74.12426 0.95000 1.85976 40.6  5* 5.926271.47140  6 8.28920 1.70000 2.14422 17.5  7 12.83109 Variable  8(Diaphragm) ∞ 0.00000  9* 4.63999 2.45000 1.80139 45.4 10 11.405980.50000 1.92286 20.9 11 4.08736 0.48000 12 11.58038 1.50000 1.80420 46.513 −46.42335 Variable 14* 16.70893 1.70000 1.80610 40.7 15 −271.10350Variable 16 ∞ 1.00000 1.51680 64.2 17 ∞ (BF) Image surface ∞

TABLE 23 (Aspherical data) Surface No. 4 K = 0.00000E+00, A4 =8.00930E−05, A6 = −8.24171E−07, A8 = 7.02480E−09 A10 = 0.00000E+00Surface No. 5 K = −2.80748E+00, A4 = 1.51170E−03, A6 = −1.93182E−05, A8= 3.79463E−07 A10 = −1.27953E−09 Surface No. 9 K = −3.81122E−01, A4 =1.92672E−05, A6 = 2.36355E−05, A8 = −5.76293E−06 A10 = 5.76364E−07Surface No. 14 K = 0.00000E+00, A4 = 5.48957E−05, A6 = 4.00480E−07, A8 =0.00000E+00 A10 = 0.00000E+00

TABLE 24 (Various data) Zooming ratio 6.54099 Wide-angle MiddleTelephoto limit position limit Focal length 6.1338 15.6371 40.1213F-number 3.35969 3.84965 5.84335 View angle 35.0631 13.8718 5.4025 Imageheight 3.8300 3.8300 3.8300 Overall length 43.0188 45.0018 57.0268 oflens system BF 0.49471 0.53782 0.50457 d3 0.5000 11.4355 18.9917 d717.0651 5.3765 1.4500 d13 3.8959 4.3424 17.9582 d15 5.6117 7.8582 2.6709Entrance pupil 12.7522 32.7502 57.3438 position Exit pupil −17.6154−20.9508 309.8164 position Front principal 16.8085 37.0083 102.6693points position Back principal 36.8850 29.3648 16.9055 points positionSingle lens data Lens Initial surface Focal element number length 1 1−74.7335 2 2 26.8298 3 4 −6.3478 4 6 17.0587 5 9 8.4064 6 10 −7.1366 712 11.6594 8 14 19.5762 Zoom lens unit data Initial Overall Lens surfaceFocal length of Front principal Back principal unit No. length lens unitpoints position points position 1 1 43.09186 3.70000 −0.63212 1.04900 24 −10.40411 4.12140 0.28566 1.75797 3 8 12.61365 4.93000 −1.725300.54757 4 14 19.57623 1.70000 0.05479 0.81105 Magnification of zoom lensunit Lens Initial Wide-angle Middle Telephoto unit surface No. limitposition limit 1 1 0.00000 0.00000 0.00000 2 4 −0.35568 −0.56805−0.96698 3 8 −0.65716 −1.29835 −1.26908 4 14 0.60898 0.49202 0.75870

The following Table 25 shows the corresponding values to the individualconditions in the zoom lens systems of each of Numerical Examples.

TABLE 25 (Values corresponding to conditions) Example Condition 1 2 3 45 6 7 8 (b-1) f_(T)/f_(w) 6.54 6.59 6.53 6.54 6.54 6.55 6.54 6.54 (a-2)ω_(w) 30.87 31.08 34.84 32.06 32.05 32.05 33.68 35.06 (2-2) f₂/f_(w)−1.60 −1.57 −1.60 −1.60 −1.53 −1.43 −1.62 −1.70 (3-2)(β_(2T)/β_(2w))/(β_(3T)/β_(3w)) 1.41 2.58 1.91 1.82 4.54 4.91 1.67 1.41(4-2) M₁/M₃ 1.09 1.11 1.02 1.20 2.90 2.21 1.26 1.26 (5) nd_(2p) 1.9462.002 1.946 2.002 2.002 2.002 2.144 2.144 (6) (r_(2na) +r_(2nb))/(r_(2na) − r_(2nb)) 0.98 0.81 0.83 0.95 0.88 0.87 0.85 0.85 (7)(r_(2nb) + r_(2pa))/(r_(2nb) − r_(2pa)) −5.17 −6.61 −6.21 −5.49 −6.00−5.52 −6.18 −6.02 (8) (r_(1pa) + r_(1pb))/(r_(1pa) − r_(1pb)) −1.33−1.20 −1.21 −1.48 −1.46 −1.40 −1.29 −1.30 (9) f₃/f_(w) 2.05 1.95 1.992.02 1.89 1.91 2.03 2.06 (10) f_(3IL)/f₃ 1.39 1.25 1.18 1.30 1.14 1.161.19 1.14 (11) f_(3n)/f₃ −0.46 −0.50 −0.50 −0.50 −0.67 −0.68 −0.55 −0.57

INDUSTRIAL APPLICABILITY

The zoom lens system according to the present invention is applicable toa digital input device such as a digital camera, a mobile telephone, aPDA (Personal Digital Assistance), a surveillance camera in asurveillance system, a Web camera or a vehicle-mounted camera. Inparticular, the zoom lens system according to the present invention issuitable for a photographing optical system where high image quality isrequired like in a digital camera.

DESCRIPTION OF THE REFERENCE CHARACTERS G1 first lens unit G2 secondlens unit G3 third lens unit G4 fourth lens unit L1 first lens elementL2 second lens element L3 third lens element L4 fourth lens element L5fifth lens element L6 sixth lens element L7 seventh lens element L8eighth lens element A aperture diaphragm P plane parallel plate S imagesurface 1 zoom lens system 2 image sensor 3 liquid crystal displaymonitor 4 body 5 main barrel 6 moving barrel 7 cylindrical cam

The invention claimed is:
 1. A zoom lens system, in order from an objectside to an image side, comprising a first lens unit having positiveoptical power, a second lens unit having negative optical power, a thirdlens unit having positive optical power, and a fourth lens unit havingpositive optical power, wherein the first lens unit is composed of atmost two lens elements, the second lens unit is composed of two lenselements, the third lens unit is composed of three lens elements, inorder from the object side to the image side, including an object sidelens element having positive optical power, a lens element havingnegative optical power, and an image side lens element having positiveoptical power, and the following conditions (b-1) and (a-2) aresatisfied:f _(T) /f _(W)>6.0  (b-1)ω_(W)≧30  (a-2) where, f_(T) is a focal length of the entire system at atelephoto limit, f_(W) is a focal length of the entire system at awide-angle limit, and ω_(W) is a half view angle (°) at a wide-anglelimit.
 2. The zoom lens system as claimed in claim 1, wherein the secondlens unit includes a lens element having positive optical power, and thefollowing condition (5) is satisfied:1.88<nd_(2p)<2.20  (5) where, nd_(2p) is a refractive index to thed-line of the lens element having positive optical power, which isincluded in the second lens unit.
 3. The zoom lens system as claimed inclaim 1, wherein the second lens unit includes a lens element havingnegative optical power, and the following condition (6) is satisfied:0.35<(r _(2na) +r _(2nb))/(r _(2na) −r _(2nb))<1.20  (6) where, r_(2na)is a radius of curvature of an object side surface of the lens elementhaving negative optical power, which is included in the second lensunit, and r_(2nb) is a radius of curvature of an image side surface ofthe lens element having negative optical power, which is included in thesecond lens unit.
 4. The zoom lens system as claimed in claim 1, whereinthe second lens unit is composed of two lens elements, in order from theobject side to the image side, including a lens element having negativeoptical power, and a lens element having positive optical power, and thefollowing condition (7) is satisfied:−8.5<(r _(2nb) +r _(2pa))/(r _(2nb) −r _(2pa))<−3.5  (7) where, r_(2nb)is a radius of curvature of an image side surface of the lens elementhaving negative optical power, which is included in the second lensunit, and r_(2pa) is a radius of curvature of an object side surface ofthe lens element having positive optical power, which is included in thesecond lens unit.
 5. The zoom lens system as claimed in claim 1, whereinthe first lens unit includes a lens element having positive opticalpower, and the following condition (8) is satisfied:−1.80<(r _(1pa) +r _(1pb))/(r _(1pa) −r _(1pb))<0.00  (8) where, r_(1pa)is a radius of curvature of an object side surface of the lens elementhaving positive optical power, which is included in the first lens unit,and r_(1pb) is a radius of curvature of an image side surface of thelens element having positive optical power, which is included in thefirst lens unit.
 6. The zoom lens system as claimed in claim 1, whereinthe following condition (9) is satisfied:1.87<f ₃ /f _(W)<3.00  (9) where, f₃ is a composite focal length of thethird lens unit, and f_(W) is a focal length of the entire system at awide-angle limit.
 7. The zoom lens system as claimed in claim 1, whereinthe following condition (10) is satisfied:0.5<f _(3IL) /f ₃<1.5  (10) where, f_(3IL) is a focal length of theimage side lens element having positive optical power, which is includedin the third lens unit, and f₃ is a composite focal length of the thirdlens unit.
 8. The zoom lens system as claimed in claim 1, wherein thethird lens unit includes a cemented lens element which is obtained bycementing the object side lens element having positive optical powerwith the lens element having negative optical power.
 9. The zoom lenssystem as claimed in claim 1, wherein the fourth lens unit comprisessolely a lens element having positive optical power.
 10. The zoom lenssystem as claimed in claim 1, wherein the following condition (11) issatisfied:−1.00<f _(3n) /f ₃<−0.25  (11) where, f_(3n) is a focal length of thelens element having negative optical power, which is included in thethird lens unit, and f₃ is a composite focal length of the third lensunit.
 11. An imaging device capable of outputting an optical image of anobject as an electric image signal, comprising: a zoom lens system thatforms an optical image of the object; and an image sensor that convertsthe optical image formed by the zoom lens system into the electric imagesignal, wherein the zoom lens system, in order from an object side to animage side, comprises a first lens unit having positive optical power, asecond lens unit having negative optical power, a third lens unit havingpositive optical power, and a fourth lens unit having positive opticalpower, wherein the first lens unit is composed of at most two lenselements, the second lens unit is composed of two lens elements, thethird lens unit is composed of three lens elements, in order from theobject side to the image side, including an object side lens elementhaving positive optical power, a lens element having negative opticalpower, and an image side lens element having positive optical power, andthe following conditions (b-1) and (a-2) are satisfied:f _(T) /f _(W)>6.0  (b-1)ω_(W)≧30  (a-2) where, f_(T) is a focal length of the entire system at atelephoto limit, f_(W) is a focal length of the entire system at awide-angle limit, and ω_(W) is a half view angle (°) at a wide-anglelimit.
 12. A camera for converting an optical image of an object into anelectric image signal and then performing at least one of displaying andstoring of the converted image signal, comprising: an imaging deviceincluding a zoom lens system that forms the optical image of the objectand an image sensor that converts the optical image formed by the zoomlens system into the electric image signal, wherein the zoom lenssystem, in order from an object side to an image side, comprises a firstlens unit having positive optical power, a second lens unit havingnegative optical power, a third lens unit having positive optical power,and a fourth lens unit having positive optical power, wherein the firstlens unit is composed of at most two lens elements, the second lens unitis composed of two lens elements, the third lens unit is composed ofthree lens elements, in order from the object side to the image side,including an object side lens element having positive optical power, alens element having negative optical power, and an image side lenselement having positive optical power, and the following conditions(b-1) and (a-2) are satisfied:f _(T) /f _(W)>6.0  (b-1)ω_(W)≧30  (a-2) where, f_(T) is a focal length of the entire system at atelephoto limit, f_(W) is a focal length of the entire system at awide-angle limit, and ω_(W) is a half view angle (°) at a wide-anglelimit.